S01E85: Clown And Out

A clown (who looks and speaks like the Jerry Lewis-esque Mr. Director) is hired by Mr. Plotz for Wakko's birthday party, but Plotz learns from Dr. Scratchansniff that, like Mr. Plotz, Wakko has a bad fear of clowns, resulting in the clown being battered and bruised. The skit has become somewhat of an internet meme.